Tubular heat exchange assembly



finite States Patent lnventor Roman Rummel Bruhl, Germany Filed April 26 1968 Patented Oct. 13, 1970 Assignee Von Roll A.(j.,

(,erlafingen, Switzerland, a corporation of Switzerland Priority May 5, 1967 Switzerland 6,431/67 TUBULAR HEAT EXCHANGE ASSEMBLY 3 Claims, 7 Drawing Figs.

US. Cl 165/163 29/157, 60/266 Int. Cl F28d 7/00 Field 01' Search 165/ 166,

156] References Cited UNITED STATES PATENTS 1 1,655,086 1/1928 Blanding 165/163 2,686,044 8/1954 Maldague i. 122/235X 3,069,850 12/1962 Ledwith et a1. 60/266 3,086,358 4/1963 Tuma\'icus..... 165/16-1X 3,130,779 4/1964 Huet 165/163 3,349,464 10/1967 Becker et a1 29/157.3X

Primary Examinew-Robert A. OLeary Assiszanz ExaminerTheophil W. Streule Attorney-Jacobi, Davidson and Kleeman ABSTRACT: A tubular heat exchange apparatus for use with two fluids, comprising, within a gas-tight casing, a plurality of tubes and two headers, said tubes being connected with such headers The tubes are arranged in one or more rows or ranges around a central duct of variable cross section. The heat exchange apparatus is adapted to convey combustion gases from a furnace or the like.

Patented bct..13, 1970 3,533,467

Sheet Z of3 V Fig. 7

g INVENTOR haw ATTORNEYS Patehted Oct. 13, 1970 Z of 3 Sheet ATTORNEY.

Patented Oct. 13, 1970 3,533,467

Sheet Z of 3 Fig.6

INVENTOR Raye/r UMMEL flea-EM I ATTORNEYJ v l TUBULAR HEATEXCHANGE ASSEMBLY BACKGROUND OF THE INVENTION The present invention relates to an improved tubular heat exchange assembly for use with two fluids, such as liquids, vapours and/or gases, and. is of the type comprising, within a gas-tight casing a plurality of tubes operably connected with two headers, one of the fluids flowing through the tubes and the other one outside and along them.

In the heat exchange assembly according to the invention, tubes of straight or curved shape are arranged so as to provide between them a central channel for the fluid flowing outside the tubes,

When that channel is narrow, the heat transmission is obviously effected essentially by convection. In heat exchange assemblies designed for increased heat transmission by radiation, that channel is widened into a radiation chamber of vertical, horizontal or inclined position, hereinafter referred to as a duct. Around ducts of uniform cross section, the tubes defining their contour may be easily arranged at equal and constant intervals over their entire length. Around ducts of variable cross section, however, the regular arrangement of the tubes is complicated by the fact that, following the variation of the cross section, the spacingor intervals between the tubes cannot be kept constant over their entire length. Larger intervals will alternate with smaller ones and even with superposed tubes. That requires a great deal of skilled work for the fabrication and thus increased costs.

Another inconvenience lies in the fact that with the tubes arranged in an irregular way, as described above, the thermal load will be different for the various tubes or even for various parts of the same tube. With high gas velocities in chambers of intense radiation, close arrangements of the tubes may even hinder the free flow of the radiating fluid.

SUMMARY OF THE INVENTION Accordingly, the present invention seeks to obviate these inconveniences.

To accomplish this objective, the invention provides a heat exchange assembly,.morespecifically for heat transmission by radiation, comprising tubes with both ends connected to respective headers, said tubes surrounding and defining a central duct of variable cross: section for a heat transmitting fluid for instance.

A particular aspect of the invention is that in a heat exchange assembly as described above, and with tubes regularly arranged side-by-side, close fitting over their entire length, one of the tubes parameters, i.e. the direction of the axis or the shape of the cross section, is for all tubes and in any plane orthogonal to the ducts axis, a single and definite function of the size of the respective cross-sectional area of the duct. I

A preferred embodiment of the heat exchange assembly according to the invention incorporates a vertical duct of variable cross section, delimitated or bounded by helicoidal tubes of variable inclination.

A further preferential embodiment of the heat exchange assembly according to the invention may incorporate at least two rows or ranges of tubes which are coaxially arranged.

Still another preferential embodiment of the heat exchange assembly teaches a vertical duct of variable but circular cross section throughout, with tubes of equal length and shape.

A still further preferential embodiment of the heat exchange assembly according to the invention embodies a vertical duct shaped as a hyperboloid of revolution, with straight tubes lying within the surface of said hyperboloid. Another feature relates to an improved process for the fabrication of a heat exchange assembly with a centralduct of variable but circular cross section throughout, using tubes of equal length and shape, all tubes being connected in identical way and arrangement with the respective headers.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood, and objects other than those set forth above, will become apparent when consideration is given to the following, detailed description thereof. Such description makes reference to the annexed drawings wherein: i 7

FIG. 1 is a longitudinal section of a heat exchange assembly with helicoidal tubes of variable inclination;

FIG. 2 is a longitudinal sectional view of a heatexchange assembly as illustrated in FIG. 3, taken along the line ll-ll thereof, with tubes shaped in accordance with their respective distance from the ducts axis; v

FIG. 3 is a transverse sectional view of a heat exchange assembly of the type illustrated in FIG. 2, and taken along the line Ill-III thereof;

FIG. 4 is a transverse sectional view of a heat exchange assembly as illustrated in FIG. 2, taken along the line IV-IV thereof;

FIG. 5 is an enlarged transverse sectional view of a heat exchange assembly as illustrated in FIG. 2 taken along the line V-V thereof; 1

FIG. 6 is a longitudinal sectional view of a heat exchange assembly with two rows or ranges of tubes which are coaxially arranged; and

FIG. 7 is a perspective representation of a hyperboloidshaped heat exchange assembly provided with straight tubes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, in FIG. 1 the heat exchange assembly depicted, by way of example, incorporates two headers l and 2 and a plurality of tubes 3 having their upper and lower ends connected with these two annular headers l and 2. The tubes 3 are located in close-fitting, side-by-side arrangement, to thus define a central duct 4 for one of the media involved in heat transmission, generally the heat transmitting medium. The circular cross section of this duct 4, which for convenience has been designated by reference numeral q, is variable in size along the ducts axis A,.

Water is fed into the lower header 1 and rises through the tubes 3, the latter acting as boiler-tubes. A mixture of hot water and steam is thereby produced in the tubes 3, collected in the upper header 2 and discharged therefrom. The openings and pipe connections provided for this purpose at both headers are not represented in FIG. 1, in order to simplify the drawings.

The heat exchange assembly, as illustrated in FIG. 1, which may be assumed to be mounted on' top of a high-temperature furnace operating with molten slag, and wherein the stream of hot combustion gases issues from said furnace with a pronounced twist or spin, will flow upwards through the duct 4 of the heat exchange assembly. Small particles entrained by the gas-stream, e.g. droplets of molten slag will be separated by increased centrifugal forces in the narrow part of the duct 4 and will flow back into the furnace along the smooth inner surface of the duct 4.

The tubes 3 are all of identical helicoidal shape, with the inclination angle a varying in dependence upon the size ofthe respective cross-sectional area 4: said variable angle of inclination being such that the tubes 3 are maintained in closefltting, side-by-side position over their whole length and that, at no place, will there occur any superposition of neighboring or contiguous tubes 3.

Thus, and with all tubes close-fitting to each other over their entire length, in any plane E orthogonal to the ducts axis A. the angle of inclination a of the axis A; of any tube 3 will depend solely upon the size of the respective cross-sectional area 4q, said angle of inclination a of the axis A; of any tube, thereby constituting a characteristic tube parameter;

- In a more general aspect, with the tubes arranged with intervals between them, the inclination angle a of the helicoidal tubes 3 will be determined both by the size of the respective cross-sectional area 4q and by the desired spacing between neighboring tubes..The inclination angle a will be greatest in the plane E of the smallest cross section -4q. with tangent a 7 possibly being infinite, so that in that plane, the tubes 3 may be arranged with their axes parallel with the ducts axis A, This is visible in FIG. 1 in the lower part of the duct 4 designated Be, comprising the smallest cross-sectional area 4q, where r=90 and tangent 11 In contrast, in the plane E with the-largest cross-sectional area 4g, the inclination angle a will be smallest; as isthe casein the upper plane marked Eg in FIG. I.

I Instead of having the tubes 3 arranged in close fit, i.e.

' be preferred, since it allows all tubes 3 to be of equal length and curvature. Circular cross sections 4q are furthermore of advantage, since the thermal load is evenly distributed at all tubes, thereby avoiding thermal stresses within the heat exchange assembly.

Around the tubes 3 there is provided a gas-tight casing which is accommodated to the longitudinal profile or shape of the duct 4. On their inner face, that is, the face actually bordering the duct 4, studs may be provided on these tubes 3 which then serve to retain or support a layer of refractory material in order to protect the tubes 3 against excessive thermal load in a manner well known in the art.

The type of heat exchange assembly shown and described in connection with FIG. I, is a short and compact construction, quite able to resist thermal shocks owing to the elasticity of the helicoidal tubes. Y

In the embodiment of tubular heat exchange assembly depicted in FIG. 2, the two headers I and 2 are connected by means of a plurality of tubes 3 which serve to define a central duct 4', with circular cross sections 4q' of variable size along the ducts'axis A The tubes 3' are curved in conformity with the longitudinal profile of the duct 4', with their axes (marked A lying in planes E, passing through the duct's axis A, (of. FIGS. 3 and 4'). For any of the identical tubes 3, the shape and size of its cross section 3q' varies in dependence upon the respective distance S between said tube 3' and'the ducts axis A,, the relationship being such that in spite of the variation of the duct's cross-sectional area 4q' the tubes remain in closefitting, side-by-side position, i.e. without any free spacing or interval and that, furthermore, at no place of the duct 4', does there occur any superposition of contiguous or neighboring tubes 3'.

Thus, with the close-fitting arrangement of the tubes 3 over their entire length, the shape of the cross sections 3q' of these tubes constitutes a characteristic tube parameter, being determined in any plane E (FIG. 2) orthogonal or perpendicular to the ducts axis A,, by the size of the cross-sectional area 4q of the duct in said plane E.

I In the region represented by reference character D anddesignating the largest cross-sectional area of the duct 4, all

tubes 3' will have a circular cross section 3q', which will be gradually flattened the nearer the tubes come to lie to the ducts axis A,, such being in direct dependence upon the size of the respective cross-sectional area 4q'.

FIG. 5 depicts in an enlarged scale the cross section 3q of such a flattened tube 3' as such occurs in the narrowest part of the duct 4, that is in the plane E with the smallest cross-sectional area 4q' (cf. section-lines IV-IV and V-V in FIG. 2). The contour of the tubes cross section is angularly flattened towards'the duct's axis, as is visualized by the two tangential lines marked T. For further illustration and comparison, the

' original circular cross section of the tube 3' is represented in dotted lines.

As in the case of the embodiment according to FIG. 1, here too, the tubes 3' are surrounded by a gas-tight casing 5 which follows the longitudinal profile of the duct 4' and once again,

the tubes 3' may be provided on their inner face with studs or the like and a layer of refractory material for protection of such tubes against excessive thermal load.

Furthermore, also as in the case of FIGI-l, here too, instead of the tubes 3' being arranged in close fit, side-by-side, that is,

without any spacing o'r intervals therebetwee'n, any desired spacing between them may be adopted-.Similarly, instead of a circular cross section 4q', any other cross-sectional shape may be adopted for the duct 4.'However, here again, ducts of circular cross section are preferable, since, not only are the tubes 3' of identical shape and length, but, besides, an even distribution of the thermal load is ensured.

The embodiment of the invention described above in conjunction with FIGS. 2 to 5 is particularly suited for lengthwise extending heat exchange assemblies. In the two embodiments of heatexchange assembly, as previously considered with regard to FIG. 1 and FIGS. 2-5, respectively, the tubes 3 and 3, respectively, serve as boiler tubes with a high thermal load. In consideration of this, it is recommended that they are located in close-fitting side-by side arrangement, that is to say, without intervals or with small intervals or spacing of not more than a few millimeters. At lower thermal loads, however, it is obvious that the tubes may be spaced from each other, that is, arranged with greater spacing or intervals, thus embracing a greater periphery with the same number of tubes. In both embodiments, spaced arrangements may be adopted, with equal spacing over the entire length of the tubes or varying in width.

In conclusion, it may be emphasized that the two principle embodiments of heat exchange assemblies as described above and by way of example, may very easily be adapted to comply with any requirements.

FIG. 6 represents a heat exchange assembly with two ranges or rows of tubes R, and R which are coaxially arranged in a duct 4" having the longitudinal axis A". These tubes R, and R, have their ends connected to two headers l and 2. The external row or range R, of the tubes 3" defining the duct 4" proper, is in principle shaped and arranged as in the embodiment according to FIGS. 2-5, with however, wider intervals between the tubes, said intervals being equal for all tubes 3". The tubes 3: of the inner row or range R placed coaxially within the duct 4" and defining a second, inner duct 4i, are similarly shaped and arranged, with equal intervals of larger width, e.g. millimeters for all tubes 3i, to thereby allow outer range R, are still more closely arranged. Both rows or ranges R, and R, may have their tubes located in coinciding or displaced position with respect to each other.

The cross-sectional area 4q of the duct 4 is variable along the ducts axis A,", but of circular shape throughout and so is the cross-sectional area 4qi of the inner duct 4i" defined by the inner range or row of tubes R Thus, in this case too, the tubes 3" of the outer range R, are all equal in length and shape and so are the tubes 3i of the inner range R The gas-tight casing 5 fits or encloses the contour of the outer tube range or row R,.

In FIG. 7 there is shown a further embodiment of the heat exchange assembly according to the present invention, with a duct marked 4 having the shape of an hyperboloid of revolution, incorporating straight tubes 3g lying within the hyperboloids surface, all tubes having the same shape and length.

It is well known that by rotation of an hyperbola around its vertical axis (y y) a continuous surface of an hyperboloid of revolution (hereinafter briefly referred to as a hyperboloid) is being generated, with straight lines entirely lying within said surface, said straight lines being inclined with regard to the rotational axis (y y).

On this mathematical property of the hyperboloid, the embodimcnt of the heat exchange assembly, represented in H6. 7, is based. Here again. with the tubes 3g arranged closefitting, side-by-side over their entire length,that is. without intervals, the direction of the tubes axes constitutes a tubeparameter for all tubes 3g in any plane E orthogonal to the axis A of the hyperboloidal duct 4 said-tube parameter depending upon the size of the cross-sectional area 4.,,, in the respective plane Eh it is further'known. that in the neck of the hyperboloid, that is in the narrowest part ofthe duct 41 111.. the distance between the axes of two contiguous tubes 3g. is a minimum. Begining from this narrowest part of the duct 4,,,,,, the distance between two contiguous tubes is increasing in a linear. i.e. continuous way, to reach a maximum at the upper and lower ends of the hyperboloid. With hyperboloids of slender profile. i.e. with a less pronounced neck, as is the case in practice, the deviation in distance along the entire length of the duct 4 is very small, so that the tubes 3g may be considered as beingat equal distances. Furthermore, since the duct 4 is of circular cross section in any sectional plane E along its entire length. equal thermal load for all tubes 3g is ensured.

At high thermal loads, the tubes have to be arranged in close fit side-by-side, as already mentioned, in other words with no spacing or intervals or with very small intervals of a few. millimeters. The embodiment with the hyperboloidshaped duct 4 fulfills this requirement, since in the neck of the duct, i.e. in the place of highest heat concentration, the distance between contiguous tubes is minimum.

Considering furthermore, that the inclination of the straight tubes 3g may be chosen either to the left or to the right, i.e. corresponding or opposed to the spin of the gas-stream issuing from the furnace, thereby increasing or reducing the initial turbulence of the gas-stream, it is obvious that the embodiment with hyperboloid-shaped duct, is adaptable to requirements as may arise in practice. I

It will be noted that in the case of the embodiment according to the H0. 7, the basic longitudinal profile of the duct 4 is predetermined by the hyperbola generating the hyperboloid in contrast to the embodiments according to FIG. 1, FIGS. 2 5 and FIG. 6. where any desired longitudinal profile is possible. However. the hyperboloidal-shaped duct is not only easily adaptable to all thermal and aerodynamical requirement. but moreover, this embodiment is advantageous in that, for ducts'with variable cross section along their axes. straight tubes 3;; of equal length may be used and arranged in close-fitting position over their entire length. Thus. expensive labor for the curved shaping of the tubes may be spared.

instead ota single row or range of tubes 3g as illustrated in FIG. 7, two or more ranges can be arranged coaxially within the hyperboloid-shaped duct 41 in' the manner already described in connection with FIG. 6.

As an alternative to the embodiments described above with the heat-transmitting fluid flowing through the duct. the position could be reversed by directing such fluid to flow through .the tubes proper. with the heat-absorbing fluid then flowing in this case through the duct.

In conclusion, the versatility of the heat exchange assembly according to the invention should be emphasized.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be variously embodied and practiced within the scope of the following claims.

lclaim:

l. A tubular heat exchange apparatus adapted to convey combustion gases from a furnace or the like, especially for heat transmission by radiation, comprising wall means defin ing a gas-tight casing, a plurality of tubes located within said gas-tight casing and in contiguous relation with said wall means, an inlet header and an outlet header at opposite ends of said casing, said plurality of tubes being operatively connected with said headers. said tubes being arranged adjacent one another throughout their entire length and defining acentral duct of variable cross section, said tubes having their lengthwise axes curved in accordance with the longitudinal profile of said duct and disposed in axial planes of said duct, and the circumferential cross-sectional shape of said tubes, varying as a function of their distance from the longitudinal axis of said duct. substantially angularly flattened toward the ducts axis in that portion of said duct wherein said tubes are closest to said longitudinal axis, whereby with high gas velocities in chambers of intense radiation the free flow of the combustion gases is not hindered.

2. A heat exchange assembly as defined in claim 1, wherein said duct is of substantially circular cross section along its entire length' and wherein said tubes possess equal length and shape.

3. A tubular heat exchange assembly as claimed in claim 2 and further including another plurality of tubes connected to said headers and arranged about said plurality of tubes, said another plurality of tubes being spaced from one another so as to provide flow passages for a heat exchange medium, both pluralities of tubes being arranged substantially coaxially with respect to the longitudinal axis of said duct. 

